THM Removal by Water Spray Aeration- Tank Top Results. Thomas F. Clark, P.E. Production Engineer Monroe County Water Authority Rochester, New York

Transcription

1 THM Removal by Water Spray Aeration- Tank Top Results Thomas F. Clark, P.E. Production Engineer Monroe County Water Authority Rochester, New York

2 Monroe County s Primary Water Supply Lake Ontario

3 Shoremont Treatment Plant

4 Webster Treatment Plant

5 MCWA Service Area

6 Genesee County Our third facility is a small (0.25 MGD) groundwater facility that delivers water into western Genesee county. District also receives purchased water.

7 Path of Water to Western Genesee District MCWA Pembroke BPS Pembroke service area Corfu Well

8 Pembroke BPS Pumping distance is approx 26 miles from Buffalo to the BPS in Pembroke. Because of travel time, THM levels coming into Pembroke can be problematic during the late summer after Lake Erie water has warmed.

9 Purchase Districts Because districts that purchase water may not have any say over how that water is treated, purchase districts can face problems with high THM levels before the water ever enters their system.

10 Historic THM Monitoring Data at Entry Point THM Concentration st 2nd 3rd 4th 1st 2nd 3rd 4th 1st 2nd 3rd 4th 1st 2nd 3rd 4th 1st 2nd 3rd 4th

11 Western Genesee District Since 2010, this spray aeration system in our Pembroke tank has provided us with a step reduction in THMs prior to rechlorination and delivery of the water further into the district.

12 THM Removal w/ Fall Distance The work done during the last two years relates to documenting THM removal at different fall distances within a tank. This was suggested by a question from a local operator.

13 Question This utility needs to keep a high water elevation in their tank to maintain adequate pressure in the distribution system. Since the water elevation will tend to be high and turnover will be low, there will be not more that 5 6 ft between the discharge of a nozzle and the water surface.

14 The Question Given the height limitations, is 6 ft fall distance sufficient to remove THMs via water spray? What about less than 6 ft? Henry s Law can be used to predict the extent of removal of THMs from water but gives no prediction on the rate at which they will be removed.

15 Our Work We set out to document the percent removal of TTHM w/ fall distances of 3 ft 6 ft 12 ft 20 ft

16 Our Work We also wanted to answer a question that has been asked many times.what is the impact on residual chlorine after passing through the spray system? Lastly, what is the effect of aeration on the water s ph?

17 Pembroke Tank Steel 500,000 gallons 37 ft diameter 61 ft high

18 Western Genesee District Historically, because of the long route taken by water to enter INTO this part of our system and then additional time to flow east, THM formation has been a problem. Town of Pembroke Genesee County, NY New York State Thruway 2954 Main Rd East Pembroke 3.5 miles 4.5 miles Pembroke Pump Station Pembroke Tank Autoflush unit To Corfu NY

19 Hypochlorite Due to the long transmission route once water leaves the tank, it is necessary to rechlorinate with sodium hypochlorite on the outflow. Dose = ~ 0.6 mg/l THM removal by water spray gives us a step reduction prior to the additional disinfection

20 Our Spray System A 7 ½ Hp variable speed pump Pump operates at about 72 gpm Pump operates to allow 4-5 day turnover rate

21 Riser Piping Sch 80 PVC pipe 2 inch diameter

22 Tank Penetration Penetration into the hatch- bulk head fitting. Pressure of psi at tank top.

23 Spray Heads

24 Tank Top From ~ 5 to 20 feet in fall distance between spray heads and water surface. No active ventilation

25 Sample Collection Points On the riser line leading up along the tank. From inside the tank

26 Sample Collection A modified telescopic dipper (with a shield) held in place at the appropriate elevation within the tank.

27 Sample Analysis THM samples were transferred to 40 ml vials with dechlorinating agent. The analysis was conducted at a NYSDOH approved laboratory. EPA Method for THM analysis Chlorine samples were performed in the field ph samples were chilled for laboratory analysis

28 Field Work Over two summers, eleven data sets were collected for fall distances of 6 ft, 12 ft and 20 ft. (Fogjet nozzle) Water temperatures at time of sampling were between 57 degrees F and 68 degrees F.

29 SMD info for the nozzles Fogjet nozzle is routinely utilized. This combines the spray capacity of seven nozzles on one head. Estimated water drop size diameter (SMD) was ~ 500 u.

30 Fogjet Nozzle Chloroform Removal in Percent Removal ft 6 ft 12 ft 20 ft

31 Dichlorobromomethane Removal in Percent Removal ft 6 ft 12 ft 20 ft

32 Dibromochloromethane Removal in Percent Removal ft 6 ft 12 ft 20 ft

33 Removal vs. Water 80 Temperature 70 THM Removal Percentage y = x R² = Water Temperature, deg F

34 Effect on ph ph of Incoming vs Sprayed Water In Sprayed

35 Effect on Chlorine Residual Chlorine Residual Into Manifold vs Sprayed at 20 ft Fall Distance Free Chlorine Residual, mg/l In Sprayed Test Number

36 Long Term THM Data in East Pembroke Water Spray STARTS 1st 2nd summer 3rd 4th 1st 2nd summer 3rd 4th 1st 2nd summer 3rd 4th 1st 2nd summer 3rd 4th 1st 2nd summer 3rd 4th 1st 2nd summer 3rd 4th

37 Aeration NYS Regulatory Impact NYS Air Quality Standards Pt Item 27- Trivial Activities Air stripping processes used on public water supply systems are trivial and exempt from permitting requirements. Your state s regulations may be different.

38 Water Spray Operation System is activated in early May until early November when the water cools Proper sanitary precautions necessary when taken off line for winter Other issues/problems loss of power alarm is necessary/sufficient electrical service Watch for non flowing orifices on nozzle head

39 You Can t Just Install and Forget

40 Cost of Components Capital Cost : $ 17,000 Includes pump and variable speed drive, flowmeter, piping and spray nozzles

41 Cost of Operation Energy costs vary during the season from 9 13 cents/kwhr At 12 cents per kwhr, we are looking at about $ 16 per day to operate the pump.

42 Thank You